It occurred to me the other day while I was taking down a deposition at our office that I understand the words a witness is saying so much easier when I'm watching their mouth as they're speaking. This is also the same reason that understanding someone with a mustache is sometimes difficult. Lipreaders have been used in important roles throughout history, including allegedly cheating in American football for the New England Patriots.
Anyone who's fluent in a language can probably lipread to some degree. It's especially helpful in determining what cuss word was said when they bleep it out on TV. But how does one improve their lipreading skills? Honestly, I'm not sure other than making it a habit to watch people's lips while they speak and correlating the two. It eventually does get easier. If that doesn't work for you, there are also people out there who teach classes on it.
I've compiled this list of links for those that want to undertake the task of improving their lipreading skills, though many may have luck with teaching themselves to lipread, as I did, just by watching others. Anyway, the long and short of it is, in non-technical terms, that making certain sounds goes along with a specific thing the mouth does, movementwise. Or Wikipedia, my super reliable source, defines it as the technique of understanding speech by visually interpreting the movements of the lips, face and tongue with information provided by the context, language, and any residual hearing.
Lipreading links I love (also alliteration)
Lipreading (or Speechreading) lots of good links and info!
How to Read Lips actually some good tips on learning to lipread, especially for a wiki
Speechreading (Lip-reading) interesting article about lipreading or speechreading
YouTube Videos on lipreading
Lip Reading Program Available Online free video with sounds that teaches some of the basic sounds
Lip Reading Lesson 1 video without audio. Great for testing your skills!
Lip Reading Lesson 2 another video without audio.
Lip Reading Lesson 3 still another video without audio. Same people as the two before. Actually, they have a ton of these videos on there, and you can see the entire list if you click on the dropdown box right below the title of the video that says (currently) 279 videos. That should keep you busy.
Charlie's Lip Reading Challenge this one's kind of cool, with audio in parts and without audio for the challenge portions
heidijwalsh's Channel a group of lipreading lessons and practice videos
So the moral of the story is watch your witness at all times without being creepy!
There's lots more out there about the valuable skill of lipreading, and this is just enough to get your feet wet. I hope this helps you understand your witnesses better and make steno easier on you!